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Interaction of Iron Chelating Agents with Clay Minerals

^a Dep. of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
^b Dep. of Microbiology and Plant Pathology, Faculty of Agricultural, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel

View larger version (18K): [in a new window]   Fig. 1. Schematic diagrams of (a) DFOB–desferrioxamine B, the free ligand of the siderophore ferrioxamine B; (b) FOB–the ferric complex of DFOB; (c) EDDHA–the free ligand of the synthetic ethylenediamine di-o-hydroxyphenylacetic acid; (d) FeEDDHA–the ferric complex of EDDHA.

View larger version (17K): [in a new window]   Fig. 2. Changes in solution concentration vs. time. (a) 1.98 mM desferrioxamine B (DFOB) and 2.04 mM the ferric complex of DFOB (FOB) with Ca-montmorillonite (results with Na-montmorillonite exhibited similar relations between DFOB and FOB). (b) FOB with Ca- and Na-montmorillonite. Experimental conditions: two replicates; 5 g L–1 clay minerals; pH 7.5; I = 0.01 M (KClO4).

View larger version (17K): [in a new window]   Fig. 3. Adsorption isotherm on Na- and Ca-montmorillonite of: (a) desferrioxamine B (DFOB); (b) the ferric complex of DFOB (FOB). Symbols represent measured values, lines represent calculated values. Experimental conditions: two replicates; 5 g L–1 clay minerals; pH 7.5; I = 0.01 M (KClO4).

View larger version (28K): [in a new window]   Fig. 4. Calculated charge of amphoteric sites of clay minerals (bold lines represent the sum of all species bearing the same type of charge—positive, negative or neutral) compared with measured values of adsorption to these minerals (dotted lines) vs. pH. (a) Ca-montmorillonite; (b) Ca-kaolinite (note different scales compared with montmorillonite in Fig. 4a). Experimental conditions: two replicates; 1.0 mM of desferrioxamine B (DFOB), the ferric complex of DFOB (FOB), ethylenediamine di-o-hydroxyphenylacetic acid (EDDHA), and FeEDDHA; 5 g L–1 clay minerals; pH values 4.0, 6.0, 7.5, 9.0; I = 0.01 M (KClO4).

View larger version (21K): [in a new window]   Fig. 5. (a) Desferrioxamine B (DFOB); (b) the ferric complex of DFOB (FOB). Calculated charge (bold lines represent the sum of all species bearing the same type of charge: positive, negative or neutral) compared to measured values of adsorption of DFOB and FOB to Ca-montmorillonite and Ca-kaolinite (dotted lines) vs. pH. Experimental conditions: 1.0 mM DFOB or FOB; 5 g L–1 clay minerals; pH values 4.0, 6.0, 7.5, 9.0; I = 0.01 M (KClO4); two replicates.

View larger version (29K): [in a new window]   Fig. 6. Desorption of desferrioxamine B (DFOB) and the ferric complex of DFOB (FOB) from Ca-montmorillonite by NaCl and CaCl2. (a) DFOB desorbed by NaCl; (b) DFOB desorbed by CaCl2; (c) FOB desorbed by NaCl; (d) FOB desorbed by CaCl2. Experimental conditions: two replicates; 0.28 mmol g–1 adsorbed DFOB or FOB, at pH 7.5; 5 g L–1 Ca-montmorillonite.

View larger version (17K): [in a new window]   Fig. 7. Changes in ethylenediamine di-o-hydroxyphenylacetic acid (EDDHA) solution concentration vs. time. Experimental conditions: two replicates; 0.544 mM EDDHA; 5 g L–1 Ca-montmorillonite. pH 7.5; I = 0.01 M (KClO4).

View larger version (24K): [in a new window]   Fig. 8. Ethylenediamine di-o-hydroxyphenylacetic acid (EDDHA) and FeEDDHA adsorption isotherms on Ca-, Na-, and Fe-montmorillonite. (a) EDDHA; (b) FeEDDHA. Experimental conditions: two replicates; 5 g L–1 clay minerals; pH 7.5; I = 0.01 M (KClO4).

View larger version (20K): [in a new window]   Fig. 9. (a) Ethylenediamine di-o-hydroxyphenylacetic acid (EDDHA); (b) FeEDDHA. Calculated charge (bold lines represent the sum of all species bearing the same type of charge–positive, negative or neutral) compared with measured values of adsorption of EDDHA and FeEDDHA to Ca-montmorillonite and Ca-kaolinite (dotted lines) vs. pH. (points for both clay minerals overlap). Experimental conditions: two replicates; 1.0 mM EDDHA or FeEDDHA; 5 g L–1 clay minerals; pH values 4.0, 6.0, 7.5, 9.0; I = 0.01 M (KClO4).